The Histology Core will provide support for histological and immunological staining of tissue samples from Projects 1-4. Appropriately prepared tissues will be embedded in paraffin or OCT for sectioning and staining. Routine histological stains will be performed. Single or 2-color immunohistochemical staining will be performed with the ABC method. For immunofluorescence, either fixed or frozen sections will be stained by Ab against lineage-specific markers for leukocyte populations, or surface costimulation molecules, adhesion molecules, receptors, and cytokines. Up to 4 color immunoflourescence staining will be performed for confocal microscopy analysis. The Histology core will also develop new reagents for studying effector cell function and development during virus infections and work closely with the Flow Cytometry Core to define Ab staining conditions and marker expression by leukocytes during virus infection. The usage of the core by the 4 projects are as follows: Project 1: Staining of mouse lung and lymph node tissues for inflammation, infiltrating cell population, and the expression of cytokine and surface receptors by CD8+ T cells, NK cells, dendritic cells, and other hematopoietic cells during influenza virus infection. Project 2: Staining of mouse liver cells for infiltrating leukocyte populations and their Ag expression and cytokine production during adenovirus infection; Reagents to block the interaction of CD8+ T cells with NK cells, dendritic cells and other cell types will be developed by the Core. Project 3: Spleen sections staining for infiltrating cells, cytokine production, and CD8+ T cell interaction with NK cells and dendritic cells during MCMV infection in susceptible and resistant mouse strains. Project 4: Staining of mouse lung and lymphoid tissues for infiltrating leukocyte subsets, surface molecules, and cytokines during influenza infection and blocking of CD8+ T cell interaction with accessory cells. The long term aim of the core is to provide support for the acquisition of immunological information on CD8+ effector cell development and function in viral infections and the influences of other cell types on CD8+ T cell functions.